The semiconductor industry's drive for higher device densities, better device performance, and lower cost has led to the development of integrated circuit transistors that are three-dimensional in the sense of making greater use of space perpendicular to the substrate surface. One such transistor is the multigate field-effect transistor, aka MuGFET, trigate FET, gate-all-around FET, pi-gate FET, omega-gate FET or FinFET. The name “FinFET” as used herein refers to all of these devices. A FinFET is a field effect transistor (FET) having a channel formed in a fin-like structure of semiconductor extending from a substrate surface. This channel geometry allows the gate to wrap around one or more sides of the channel and/or act on the channel from its sides. This improves control over the channel and reduces short channel effects in comparison to a more conventional structure in which a single plane separates the channel from its gate. The fin-like structure also allows the channel to be extended vertically, increasing its cross-sectional area and permitting a higher current without increasing the transistor's footprint.
Another way to permit a transistor to support a higher current without increasing its footprint is to induce strain in the channel. A compressive strain increases charge carrier mobility in a p-type metal oxide semiconductor field effect transistor (pMOS) channel and a tensile strain increases charge carrier mobility in an n-type metal oxide semiconductor field effect transistor (nMOS). Channel strain is typically induced by forming trenches in the source and drain regions adjacent the channel and epitaxially growing within the trenches a semiconductor having a lattice constant different from that of the channel. SiGe has a larger lattice constant than silicon and can be grown in the source and drain regions to induce compressive strain for silicon-based pMOS devices. SiP or SiC has a smaller lattice constant than silicon and can be grown in the source and drain regions to induce tensile strain for silicon-based nMOS devices.